Conventional air conditioning design theories were challenged in the 1990's by a series of innovative thoughts developed by the late Dr Allan Shaw. These thoughts culminated with the air conditioning control system described in Dr Shaw's U.S. Pat. No. 6,269,650. This patent, and the system it describes, is now owned by the present applicant and will be referred to throughout this specification as the “Shaw system”.
The Shaw system is a system that operates air conditioning functions in parallel to separate the process of treating latent loads (typically to remove moisture from outdoor air) and sensible loads (typically internal air which is dry). The Shaw system differs from conventional air conditioning processes in that, rather than drawing untreated outdoor air and then cooling it within the total air conditioning system, incoming outdoor air is pre-treated (dehumidified and cooled) by a first, separate outdoor-air heat exchanger before being merged with typically dry (treated or untreated) inside air that generally has been cooled. The two air streams are merged, to be then delivered to the conditioned space.
The Shaw system is a twin heat exchanger system that provides the additional benefit of permitting the passage of the same cooling medium stream (typically water) through both heat exchangers in series to maximize efficiency. This twin heat exchanger process also avoids the traditional need for high energy inputs on two levels, firstly to overcool and then to re-heat air in order to maintain a desired level of humidity in a conditioned space. Coupled with a control system that permits integrated control of humidity, temperature and chiller operation, it has proven to be possible for the air treatment processes of the Shaw system to optimize energy performance at all times in the operating cycle to provide significantly reduced energy consumption and accurate control over humidity and temperature fluctuations in a conditioned space.
However, the Shaw system was designed for the reasonably typical cooling situations where a building's requirements only dictate the use of standard amounts of ventilation (such as about 10 to 20% outdoor air) and only needs to produce an environment in accordance with reasonably standard comfort levels. Indeed, at ventilation levels of outdoor air up to about 25%, and for typically average conditioned space temperature and humidity aims, the Shaw system has been found to operate successfully to provide the above benefits.
On the other hand, for specialist applications where the ventilation requirements require the use of higher levels of outdoor air (such as in hospitals and specialist laboratories, where levels of outdoor air of 40 to 50% are generally required), it has been found that the Shaw system has a tendency to overcool the conditioned space. Also, the Shaw system may still encounter energy inefficiencies if required to produce, for example, abnormal levels of dehumidification such as would be required to provide very low dew point temperatures. It has thus been an aim of the present invention to provide improvements to the Shaw system that allow ready adoption of the Shaw system in situations such as these, and also in situations where there is a need to provide and control multiple thermal zones within the conditioned space with individual dry bulb and general absolute humidity control.
Before turning to a summary of the present invention, it must be appreciated that the above description of the prior art has been provided merely as background to explain the context of the invention. It is not to be taken as an admission that any of the material referred to was published or known, or was a part of the common general knowledge in Australia or elsewhere.